Memory cells including top electrodes comprising metal silicide, apparatuses including such cells, and related methods

ABSTRACT

Memory cells (e.g., CBRAM cells) include an ion source material over an active material and an electrode comprising metal silicide over the ion source material. The ion source material may include at least one of a chalcogenide material and a metal. Apparatuses, such as systems and devices, include a plurality of such memory cells. Memory cells include an adhesion material of metal silicide between a ion source material and an electrode of elemental metal. Methods of forming a memory cell include forming a first electrode, forming an active material, forming an ion source material, and forming a second electrode including metal silicide over the metal ion source material. Methods of adhering a material including copper and a material including tungsten include forming a tungsten silicide material over a material including copper and treating the materials.

TECHNICAL FIELD

Embodiments of the present disclosure relate to memory cells with topelectrodes comprising metal silicide. More specifically, embodiments aredirected to conductive bridge random access memory (CBRAM) cells anddevices and methods of making the same.

BACKGROUND

In recent years, the computer memory industry is pursuing alternativememory types to replace or supplement memory devices such as dynamicrandom access memory (DRAM), Flash memory, etc. One of these alternativememory types is conductive bridging random access memory (“CBRAM”), alsoknown as programmable metallization cell (“PMC”) memory. A variety ofCBRAM cells and methods of forming them are known in the art.

As an example, a CBRAM cell conventionally includes opposing electrodeson opposite sides of an active material, such as a chalcogenide glass oran oxide glass. The active material is commonly referred to as a solidelectrolyte material. A first electrode (e.g., the inert electrode)includes a relatively inert metal (e.g., tungsten) and a secondelectrode (e.g., the active electrode) includes an electrochemicallyactive metal (e.g., silver or copper). In such a conventional CBRAMcell, the second electrode functions as an ion source material. Theresistance of the active material may be changed by applying a voltageacross the opposing electrodes. Upon application of a voltage across theelectrodes with a positive bias on the second electrode, silver orcopper cations drift from the second electrode into the active materialand are electrochemically reduced by electrons from thenegatively-charged first electrode. The reduced silver or copper atomsare electro-deposited on the first electrode, and the electro-depositionprocess continues until the silver or copper atoms form a path of lessresistance (also referred to as a “conductive bridge,” “dendrite,” or“filament”) across the active material. The conductive bridge may remainin place for an indefinite period of time, without needing to beelectrically refreshed or rewritten. Therefore, CBRAM may be referred toas a non-volatile memory.

The formation of the conductive bridge may be reversed, however, byapplying a voltage with a reversed polarity (compared to the voltageused to form the conductive bridge) to the electrodes. When a voltagewith a reversed polarity is applied to the electrodes, the metallicatoms or atomic clusters that form the conductive bridge are oxidizedand migrate away from the conductive bridge into the active material andeventually to the second electrode, resulting in the removal of the lowresistance path. Data in the CBRAM cell may be “read” by measuring theresistance between the electrodes. A relatively high resistance value(due to the lack of a conductive bridge between the opposing electrodes)may result in a certain memory state, such as a “0.” A relatively lowresistance value (due to the presence of a conductive bridge between theopposing electrodes) may result in a different memory state, such as a“1.”

A CBRAM cell is formed by positioning an active material between a firstelectrode (e.g., an inert electrode, a bottom electrode) and a secondelectrode (e.g., an active electrode, a top electrode). The firstelectrode may be formed of any sufficiently inert conductive material,such as tungsten, titanium nitride, tantalum nitride, etc. The activematerial conventionally includes a chalcogenide (i.e., including sulfur,selenium, or tellurium) glass or an oxide glass. The second electrodemay be formed of an active metal, such as silver or copper, or may beformed of a combination of a conductive ion source material and an inertmetal cap of, for example, tungsten, titanium nitride, tantalum nitride,etc. The ion source material, if present, conventionally includes anactive metal species (e.g., silver or copper) and is formed between theactive material and the metal cap. The ion source material may provideions for forming a conductive bridge across the active material whenproper voltage is applied to the CBRAM cell.

In conventional configurations, an interface between the metal cap andthe ion source material, when present, may be characterized byphysisorption and little intermixing between the elements at theinterface. Internal stresses in the materials of the CBRAM cell,combined with the characteristics of the interface, may cause at leastone of adhesive failure and deformation of materials in the CBRAM cell.Poor adhesion and deformation cause problems with or prohibit devicefabrication and memory cell performance. Accordingly, a CBRAM cell thatreduces or eliminates adhesive failure and deformation is disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial cross-sectional view of an embodiment of a CBRAMcell according to the present disclosure.

FIGS. 2A through 2D illustrate an embodiment of a method of forming aCBRAM cell, such as the CBRAM cell of FIG. 1.

FIG. 3 shows a partial cross-sectional view of an embodiment of aportion of a CBRAM cell according to the present disclosure.

FIG. 4 shows a partial cross-sectional view of another embodiment of aportion of a CBRAM cell according to the present disclosure.

FIG. 5 shows a partial cross-sectional view of another embodiment of aportion of a CBRAM cell according to the present disclosure.

FIG. 6 shows a partial cross-sectional view of another embodiment of aportion of a CBRAM cell according to the present disclosure.

FIG. 7 is a scanning electron microscopy (SEM) image of a CBRAM stackcross section of a control sample.

FIG. 8 is a SEM image of a CBRAM stack cross section formed by anembodiment of the present disclosure, such as the method illustrated inFIGS. 2A through 2D.

FIG. 9 is a graph, which shows the concentration of various elements ina CBRAM stack similar to that shown in FIG. 7 as a function of thelocation in the CBRAM stack.

FIG. 10 is a graph, which shows the concentration of various elements ina CBRAM stack similar to that shown in FIG. 8 as a function of thelocation in the CBRAM stack.

FIG. 11 is a simplified block diagram of a memory device including amemory array of one or more embodiments of the CBRAM cell describedherein.

FIG. 12 is a simplified block diagram of a system implemented accordingto one or more embodiments described herein.

DETAILED DESCRIPTION

The following description provides specific details, such as materialtypes, material thicknesses, and processing conditions in order toprovide a thorough description of embodiments of the present disclosure.However, a person of ordinary skill in the art will understand that theembodiments of the present disclosure may be practiced without employingthese specific details. Indeed, the embodiments of the presentdisclosure may be practiced in conjunction with conventional fabricationtechniques employed in the industry.

The fabrication processes described herein do not describe a completeprocess flow for processing memory device structures. The remainder ofthe process flow is known to those of ordinary skill in the art.Accordingly, only the methods and memory device structures necessary tounderstand embodiments of the present disclosure are described herein.

As used herein, the term “apparatus” means and includes a device, suchas a memory device (e.g., a CBRAM device), or a system that includessuch a device.

As used herein, the term “substantially” in reference to a givenparameter means and includes to a degree that one skilled in the artwould understand that the given parameter, property, or condition is metwith a small degree of variance, such as within acceptable manufacturingtolerances.

As used herein, any relational term, such as “first,” “second,” “over,”“top,” “bottom,” “underlying,” etc., is used for clarity and conveniencein understanding the disclosure and accompanying drawings and does notconnote or depend on any specific preference, orientation, or order,except where the context clearly indicates otherwise.

As used herein, the term “forming” means and includes any method ofcreating, building, or depositing a material. For example, forming maybe accomplished by atomic layer deposition (ALD), chemical vapordeposition (CVD), physical vapor deposition (PVD), sputtering,co-sputtering, spin-coating, diffusing, depositing, growing, or anyother technique known in the art of semiconductor fabrication. Dependingon the specific material to be formed, the technique for fanning thematerial may be selected by a person of ordinary skill in the art.

The embodiments described in the present disclosure include CBRAM cells,apparatuses including CBRAM cells, methods of forming CBRAM cells, andmethods of adhering materials in CBRAM cells. The CBRAM cells of thepresent disclosure include an electrode (e.g., a first electrode, anactive electrode, a top electrode) or portion of an electrode structureincluding a metal silicide, which provides improved adhesion between theelectrode and an ion source material underlying the electrode, as willbe described in more detail below. An interface between the metalsilicide of the electrode and the ion source material may exhibitimproved adhesion due at least in part to an increase in intermixingbetween the materials of the electrode and the materials of the ionsource material, reduced mechanical stress at the interface, and greaterchemical bonding (e.g., chemisorption) between materials across theinterface. In some embodiments, the metal silicide of the electrode maybe silicon-rich, as described in more detail below.

Although the embodiments described in the present disclosure relategenerally to CBRAM cells, one of ordinary skill in the art willunderstand that the methods and apparatuses taught by the presentdisclosure may be applied to other memory types and configurations. Forexample, teachings from the present disclosure may be applied tophase-change random-access memory (PCRAM), programmable metallizationcell (PMC) memory, resistive random-access memory (RRAM), etc.Furthermore, teachings from the present disclosure may be applied tomemory having a so-called “cross-point” architecture or a so-called“confined cell” architecture.

Embodiments of the present disclosure including one or more CBRAM cellsare shown by way of example in FIGS. 1 through 5. Similar structures orcomponents in the various drawings may retain the same or similarnumbering for the convenience of the reader; however, the similarity innumbering does not mean that the structures or components arenecessarily identical in size, composition, configuration, or otherproperty.

An embodiment of a CBRAM cell 100 is illustrated in FIG. 1 and isdescribed as follows. The CBRAM cell 100 may include a first electrode102, a dielectric material 103, a conductive material 105 disposed in anopening 104 in the dielectric material 103, an active material 106, aion source material 107, an interfacial region 108, and a secondelectrode 109 including a metal silicide, as shown in FIG. 1.

The first electrode 102 (e.g., a bottom electrode, an inert electrode, acathode) may include a conductive material, such as, for example, one ormore of tungsten (“W”), nickel (“Ni”), tungsten nitride (“WN”), titaniumnitride (“TiN”), tantalum nitride (“TaN”), polysilicon, and a metalsilicide (e.g., WSi_(x), TiSi_(x), CoSi_(x), TaSi_(x), MnSi_(x), where xis a rational number greater than zero). In some embodiments, the firstelectrode 102 may be a region of a semiconductor substrate doped so asto be electrically conductive. The first electrode 102 may be or be apart of a so-called “inert electrode” of a CBRAM cell.

The dielectric material 103 may be positioned over the first electrode102 to isolate at least portions of the first electrode 102 from theactive material 106 positioned over the dielectric material 103. By wayof example and not limitation, the dielectric material 103 may includeat least one of silicon nitride (e.g., Si₃N₄) and silicon oxide (e.g.,SiO₂). The dielectric material 103 may be any dielectric materialconfigured to electrically isolate at least portions of the firstelectrode 102 from other materials formed over the dielectric material103, as will be described in more detail below.

The dielectric material 103 may have the opening 104 in which theconductive material 105 may be disposed for providing electrical contactbetween the first electrode 102 and the active material 106 positionedover the dielectric material 103. The conductive material 105 may be theinert electrode contact of the CBRAM cell 100 and may include, by way ofnon-limiting example, one or more of W, Ni, WN, TiN, TaN, polysilicon, ametal silicide, etc.

The active material 106 may be positioned over the dielectric material103 and in electrical contact with the first electrode 102 through theconductive material 105. The active material 106 may be an oxidematerial (e.g., an oxide glass), such as at least one of a transitionmetal oxide (e.g., HfO_(x), ZrO_(x), WO_(x), etc.), a silicon oxide(e.g., SiO₂), and an aluminum oxide (e.g., Al₂O₃), or a chalcogenidematerial (e.g., a chalcogenide glass). A chalcogenide material mayinclude at least one of the chalcogen elements, such as sulfur (S),selenium (Se), and tellurium (Te).

The ion source material 107 may be positioned over the active material106 and may be electrically conductive. The ion source material 107 mayinclude an active metal species (e.g., copper or silver) for providingmetal ions that drift into the active material 106 upon application of avoltage across the CBRAM cell 100 to form a conductive bridge throughthe active material 106. By way of example and not limitation, in someembodiments, the ion source material 107 may include copper. The ionsource material 107 may also include a chalcogenide material. In someembodiments, the ion source material 107 may include at least one oftellurium and germanium. In some embodiments, the ion source material107 may include, but is not limited to, a copper-tellurium (CuTe)material, a copper-tellurium-germanium (CuTeGe) material, or acopper-tellurium-silicon (CuTeSi) material. In other embodiments, theion source material 107 may include, but is not limited to, a silvermaterial (Ag), a silver-sulfur material (AgS), or a silver-seleniummaterial (AgSe).

The active material 106 and the ion source material 107 may be formedand configured such that metal ions from the ion source material 107 maybe flowable (e.g., movable) in the active material 106 upon applicationof a voltage (e.g., a threshold voltage) across the active material 106.

The second electrode 109 (e.g., a top electrode, an anode) may bepositioned over the ion source material 107. The second electrode 109may include a metal silicide (e.g., WSi_(x), TiSi_(x), CoSi_(x),TaSi_(x), MnSi_(x), RuSi_(x), NiSi_(x), where x is a rational numbergreater than or equal to 1). The composition of the metal silicide ofthe second electrode 109 may be, for example, substantially homogeneousacross a thickness thereof. The silicon content of the metal silicidemay be substantially homogeneous across a thickness of the secondelectrode 109. The silicon in the metal silicide of the second electrode109 may improve intermixing of materials between the second electrode109 and the ion source material 107 compared to conventionalconfigurations in which the second electrode does not include the metalsilicide, as will be explained in more detail below. An interfacialregion 108 may exist at an interface between the ion source material 107and the second electrode 109. The interfacial region 108 may include acontinuous or discontinuous layer formed as a reaction product of thematerials of the ion source material 107 and of the second electrode109.

The metal silicide of the second electrode 109 may includestoichiometric amounts of silicon and the metal or may be silicon-richto provide silicon atoms for bonding with the ion source material 107.As used herein, the phrase “silicon-rich” refers to a greater number ofsilicon atoms in a mixture of silicon and the metal than is needed toprovide a stoichiometric ratio with the metal. By way of example and notlimitation, the chemical formula for stoichiometric tungsten silicide isWSi₂, indicating that there are two silicon atoms for every tungstenatom. A silicon-rich tungsten silicide may have more than two siliconatoms for every tungsten atom. Thus, a silicon-rich tungsten silicidemay have the chemical formula of WSi_(x), where x is a rational numbergreater than two. By way of example, a silicon-rich tungsten silicidemay have a ratio of number of silicon atoms to number of tungsten atoms(Si:W) of between about 2.1:1 and about 3.5:1. In some embodiments, theratio of the number of silicon atoms to number of tungsten atoms may bebetween about 2.4:1 and about 3.0:1. In one embodiment, the ratio may beabout 2.7 silicon atoms per tungsten atom.

Compared to conventional CBRAM cells lacking a metal silicide in thesecond (e.g., active) electrode, the CBRAM cell 100 including metalsilicide in the second electrode 109 may at least one of: improveadhesion between the second electrode 109 and the ion source material107; provide greater intermixing of the materials of the secondelectrode 109 and the ion source material 107 across the interfacebetween the second electrode 109 and the ion source material 107;provide a broader interfacial region 108; and reduce interfacialstress(es) between the materials of the CBRAM cell 100 of the presentdisclosure. Each of these characteristics may provide improvedmanufacturability and/or device performance of the CBRAM cell 100 and amemory device including the CBRAM cell 100.

Accordingly, a memory cell is described including a first electrode, anactive material in electrical contact with the first electrode, an ionsource material over the active material, and a second electrodeincluding a metal silicide over the ion source material. The metalsilicide of the second electrode may be silicon-rich. The metal silicideof the second electrode may be substantially homogeneous. The activematerial may be an oxide material or a chalcogenide material. The memorycell may also include a dielectric material between the first electrodeand the active material.

An embodiment of a method of forming the CBRAM cell 100 (FIG. 1) isillustrated in FIGS. 2A through 2D and is described as follows. Formingthe CBRAM cell 100 includes forming the first electrode 102, forming theactive material 106, forming the ion source material 107, and formingthe second electrode 109 including the metal silicide over the ionsource material 107, as will be described in more detail below.

Referring to FIG. 2A, the first electrode 102 may be formed of anelectrically conductive material. The first electrode 102 may be formedover or in a substrate (not shown), such as a semiconductor substrate.The formation of the first electrode 102 may be accomplished byconventional techniques and is, therefore, not described in detail inthe present disclosure.

With continued reference to FIG. 2A, the dielectric material 103 may beformed over the first electrode 102. By way of example and notlimitation, the dielectric material 103 may be formed of at least one ofsilicon nitride (e.g., Si₃N₄) and silicon oxide (e.g., SiO₂). Thedielectric material 103 may be formed by conventional techniques and is,therefore, not described in detail in the present disclosure. In oneembodiment, the dielectric material 103 may be formed by forming siliconnitride over the first electrode 102. At least one opening 104 may beformed through the dielectric material 103 by conventional methods(e.g., photolithography) and at least partially filled with a conductivematerial 105 (e.g., TiN) to provide electrical connection between thefirst electrode 102 and the active material 106 formed over thedielectric material 103, as will be described in more detail below. Theconductive material 105 may be deposited in the opening 104 and polished(e.g., by chemical mechanical planarization).

Referring now to FIG. 2B, the active material 106 may be formed over thedielectric material 103 and the conductive material 105. The activematerial 106 may be configured to enable metal ions to move (e.g.,drift) therein responsive to a voltage applied across the activematerial 106. The active material 106 may be an oxide material (e.g., anoxide glass), such as, for example, at least one of a transition metaloxide (e.g., HfO_(x), ZrO_(x), WO_(x), etc.), a silicon oxide (e.g.,SiO₂), an aluminum oxide (e.g., Al₂O₃), or a chalcogenide material(e.g., a chalcogenide glass). The active material 106 may be formed byconventional methods known in the art and not described herein indetail. By way of example and not limitation, the active material 106may be formed by at least one of PVD, CVD, and ALD techniques.

As illustrated in FIG. 2C, the ion source material 107 may be formedover the active material 106. The ion source material 107 may be formedfrom a chalcogenide material including at least one of the chalcogenelements, such as sulfur (S), selenium (Se), and tellurium (Te). The ionsource material 107 may also be formed to include an active metalspecies, such as copper (Cu) or silver (Ag), within the chalcogenidematerial for providing ions to the active material 106 when a voltage isapplied across the active material 106. The ion source material 107 maybe formed by conventional methods known in the art and not describedherein in detail. By way of example and not limitation, the ion sourcematerial 107 may be formed by at least one of PVD, CVD, and ALDtechniques.

As illustrated in FIG. 2D, the method of forming the CBRAM cell 100 mayinclude forming the second electrode 109 (e.g., a top electrode, anactive electrode, an anode) over the ion source material 107. The secondelectrode 109 may be formed of a metal silicide (e.g., WSi_(x),TiSi_(x), CoSi_(x), TaSi_(x), MnSi_(x), RuSi_(x), NiSi_(x), where x is arational number greater than zero). The structure may be heated (e.g.,annealed) during the formation of the second electrode 109 or after theformation of the second electrode 109 to react at least some of thematerials at the interface between the second electrode 109 and the ionsource material 107 to form the interfacial region 108 (FIG. 1).

Accordingly, a method of forming a memory cell (e.g., a CBRAM cell) isdisclosed including forming a first electrode, forming an activematerial, forming an ion source material comprising a chalcogenidematerial and a metal, and forming a second electrode including metalsilicide over the ion source material. Forming the second electrodeincluding metal silicide may include forming a homogeneous, silicon-richtungsten silicide material. Alternatively, forming the second electrodeincluding metal silicide may include forming a heterogeneous metalsilicide material, as will be described in more detail below. The methodmay also include forming an adhesion material at an interface betweenthe second electrode and the ion source material, as will be describedin more detail below.

The CBRAM cell 100 formed by such a method may exhibit improved adhesionand/or reduced internal stress(es) in the materials of the CBRAM cell100 when compared to CBRAM cells formed by conventional methods. Withoutbeing bound by theory, the improved adhesion may be due to controlledinterfacial bonding between the silicon of the second electrode 109 andone or more elements of the ion source material 107. For example, thesilicon of the second electrode 109 may react with one or more elementsof the ion source material 107 at an interface thereof, increasing theintermixing of the material of the second electrode 109 and the materialof the ion source material 107. This reaction may form the interfacialregion 108 (FIG. 1), which may include a continuous or a discontinuouslayer of the reaction product of the silicon of the metal silicide andone or more elements of the ion source material 107. The interfacialregion 108 may be broader in the CBRAM cell 100 formed by methods of thepresent disclosure than an interfacial region in a CBRAM cell formed byconventional methods. The interface between the second electrode 109including the metal silicide and the ion source material 107 may, thus,be chemisorbed rather than physisorbed as in conventional CBRAM cells.At a desired operating temperature of a device including the CBRAM cell100, the materials of the second electrode 109 may at least partiallyintermix with the metal of the ion source material 107 across theinterface.

Although the CBRAM cell 100 of FIG. 1 has been described as including asecond electrode 109 formed of homogeneous metal silicide, the presentdisclosure is not so limited. By way of example, FIGS. 3 through 6 showother embodiments of the present disclosure with improved adhesionbetween the second electrode 109 and the ion source material 107. Forconvenience and clarity, the interfacial region 108, the active material106, the dielectric material 103, the conductive material 105, and thefirst electrode 102 are omitted from FIGS. 3 through 6.

FIG. 3 shows an embodiment of the present disclosure including an ionsource material 107 and a second electrode 109′ formed of asilicon-rich, non-homogeneous (e.g., heterogeneous) metal silicide. Inother words, the second electrode 109′ of FIG. 2 may have a variableconcentration of silicon across a thickness of the second electrode109′. The second electrode 109′ may include a gradient of silicon acrossa thickness thereof. For example, there may be a higher concentration ofsilicon in a portion of the second electrode 109′ closer to (i.e.,proximal to) the ion source material 107 than a concentration of siliconin a portion of the second electrode 109′ more distant from the ionsource material 107. The second electrode 109′ with a variableconcentration of silicon across its thickness may be formed byco-sputtering, for example. Co-sputtering is known in the art and is,therefore, not explained in detail in this disclosure. The secondelectrode 109′ may, for example, provide silicon atoms for bonding withthe ion source material 107 while improving conductivity in otherportions of the second electrode 109′ (i.e., a portion relativelyfarther away from the ion source material 107).

FIG. 4 shows another embodiment of the present disclosure including anion source material 107, a second electrode 109, and an adhesionmaterial 110 a at an interface between the ion source material 107 andthe second electrode 109. The adhesion material 110 a may be in contactwith both the ion source material 107 and the second electrode 109. Theadhesion material 110 a may be a metal silicide and may be silicon-rich,as described above. The metal silicide adhesion material 110 a mayprovide improved adhesion between the ion source material 107 and thesecond electrode 109 without the need for forming the entire secondelectrode 109 of the metal silicide having the same concentration ofsilicon. For example, in some embodiments, the adhesion material 110 amay be formed of a metal silicide with one concentration of silicon(e.g., a relatively high concentration) and the second electrode 109 maybe formed of a metal silicide with another concentration of silicon(e.g., a relatively low concentration, a stoichiometric metal silicide,etc.). Such an adhesion material 110 a may, therefore, provideadvantages in cost and device performance (e.g., conductivity of thesecond electrode 109), for example.

FIG. 5 shows another embodiment of the present disclosure including anion source material 107, a second electrode 109, and an adhesionmaterial 110 b at an interface between the ion source material 107 andthe second electrode 109. The adhesion material 110 b may be in contactwith both the ion source material 107 and the second electrode 109. Theadhesion material 110 b may be silicon. The silicon adhesion material110 b may provide improved adhesion between the ion source material 107and the second electrode 109.

FIG. 6 shows yet another embodiment of the present disclosure includinga ion source material 107, a second electrode 109″, and an adhesionmaterial 110 c at an interface between the ion source material 107 andthe second electrode 109″. The second electrode 109″ may be a metalmaterial, such as tungsten, ruthenium, platinum,cobalt-tungsten-phosphorous, titanium nitride, tungsten nitride, ortantalum nitride, rather than a metal silicide as described above. Theadhesion material 110 c may be formed of a metal silicide and may be incontact with both the ion source material 107 and the second electrode109″. For example, the adhesion material 110 c may be formed by formingthe metal silicide over the ion source material 107 by conventionalmethods and forming the second electrode 109″ over the adhesion material110 c. The metal silicide of the adhesion material 110 c may besilicon-rich, as described above. The metal of the metal silicide of theadhesion material 110 c may be the same element as the metal of thesecond electrode 109″.

In the embodiments of FIGS. 5 and 6, the ion source material 107, theadhesion material 110 b, 110 c, and the second electrode 109, 109″ maybe heated to diffuse silicon atoms (from the adhesion material 110 b,110 c) into the ion source material 107 and into the second electrode109, 109″. The silicon atoms may react with at least one element fromthe ion source material 107 and with at least one element from thesecond electrode 109, 109″. Accordingly, a metal silicide (not shown)may be formed in at least portions of one or both of the ion sourcematerial 107 and the second electrode 109, 109″. Thus, even in anembodiment in which the second electrode 109″ is initially formed of ametal (i.e., without metal silicide), the presence of the adhesionmaterial 110 c and the heating may enable the metal of the secondelectrode 109″ to react with the silicon of the adhesion material 110 cand form the metal silicide in at least a portion of the secondelectrode 109″. Such a configuration may, therefore, enablechemisoprtion and improved intermixing of the materials at or across theinterface of the ion source material 107 and the second electrode 109,109″, as described in more detail below.

Accordingly, a memory cell (e.g., a CBRAM cell) of the presentdisclosure may include a first electrode, an active material inelectrical contact with the first electrode, an ion source material overthe active material, a second electrode formed of an elemental metalover the ion source material, and an adhesion material including a metalsilicide positioned between the ion source material and the secondelectrode. The metal of the metal silicide adhesion material may be thesame element as the metal of the second electrode.

Although FIGS. 1 and 2D through 5 show discrete boundaries between theion source material 107 and the second electrode 109 (and optionally theadhesion material 110 a, 110 b, 110 c or the interfacial region 108) forclarity, in some embodiments the boundaries between the materials maynot be discrete. In other words, materials at the interface may bepartially diffused into adjacent materials. For example, reaction of thesilicon of the metal silicide of the second electrode 109 with at leastone element of the ion source material 107 may cause some intermixing ofthe materials across the interface between the ion source material 107and the second electrode 109. Accordingly, the interface between the ionsource material 107 and the second electrode 109 may include a gradualchange in concentration (e.g., a gradient) of the various materials, asopposed to a discrete change from one material to another. Thus, thepresence of the migration and bonding of the various materials mayimprove adhesion between the ion source material 107 and the secondelectrode 109.

Referring again to FIGS. 1 through 6, a method of adhering a materialincluding copper and a material including tungsten is also disclosed. Afirst electrode 102 may be formed on a substrate (not shown) and anactive material 106 may be formed over the first electrode 102, theactive material 106 in electrical contact with the first electrode 102(e.g., through the conductive material 105). A material including coppermay be formed as the ion source material 107 and a tungsten silicidematerial (i.e., a material including tungsten) may be formed as thesecond electrode 109 over the material including copper. The materialincluding copper and the tungsten silicide material may be treated(e.g., heated, annealed) to intermix and/or react at least one of copperfrom the material including copper, tungsten from the tungsten silicidematerial, and silicon from the tungsten silicide material across aninterface between the material including copper and the tungstensilicide material. Forming the material including copper may include,for example, forming a chalcogenide material with copper ions diffusedtherein as the ion source material 107. Forming the tungsten silicidematerial may include forming a silicon-rich tungsten silicide materialas the second electrode 109, as described above. The adhesion material110 a, 110 b, 110 c including one of silicon and tungsten silicide maybe formed between the material including copper and the tungstensilicide material. By forming the second electrode 109 from tungstensilicide, the CBRAM device 100 may exhibit improved adhesion between thematerial including copper and the tungsten silicide material.

Accordingly, a method of adhering a material including copper to amaterial including tungsten is described including forming firstelectrode on a substrate, forming an active material in electricalcontact with the first electrode, forming a material including copper,forming a tungsten silicide material over the material including copper,and treating the material including copper and the tungsten silicidematerial to intermix at least one of copper, tungsten, and siliconacross an interface between the material including copper and thetungsten silicide material. Forming the material including copper mayinclude forming a chalcogenide material including copper. Forming thetungsten silicide material may include forming a substantiallyhomogeneous silicon-rich tungsten silicide material. Alternatively,forming the tungsten silicide material may include forming asilicon-rich tungsten silicide material with variable concentrations ofsilicon across a thickness of the tungsten silicide material, such as ahigher concentration of silicon in a region of the tungsten silicideproximal to the material including copper. The method may furtherinclude forming an adhesion material of silicon or tungsten silicidebetween the material including copper and the tungsten silicidematerial.

FIG. 7 is an SEM image of a cross section of a control experimentalCBRAM stack 10 including a bottom electrode 12 of tungsten, a dielectricmaterial 13 of silicon nitride, an active material 16 of zirconiumoxide, an ion source material 17 including copper and tellurium, and atop electrode 19 of tungsten. Each material was formed at a thickness ofbetween about 200 Å and about 300 Å, except for the active material 16,which was formed at a thickness of about 20 Å. The CBRAM stack 10 washeated to a temperature of about 270° C. to simulate subsequentprocessing conditions. Although the materials were each initially formedin a substantially planar configuration, the tungsten of the topelectrode material 19 deformed after exposure of the CBRAM stack 10 toheat, as can be seen in FIG. 6. Portions of the ion source material 17also shifted (i.e., were extruded) to conform to the deformed topelectrode 19. Therefore, the ion source material 17 in the CBRAM stack10 is not of uniform thickness. Due to the deformation, an apparatusincluding a plurality of CBRAM cells formed from the CBRAM stack 10 ofFIG. 6 may have poor and unpredictable performance, or may not functionat all. Furthermore, the CBRAM stack 10 has a curved (e.g., non-planar)upper surface, which may affect the ability to uniformly etch the CBRAMstack 10 in subsequent processing, such as to form individual CBRAMcells. In other control samples (not shown) having a top electrode oftungsten, adhesive failure was observed at the interface between the topelectrode and an underlying ion source material.

Without being bound to a particular theory, it is believed that internalstress in the tungsten of the top electrode 19 combined with littleintermixing of materials across the interface between the top electrodematerial 19 and the ion source material 17 contributed to the observeddeformation (and adhesive failure in other control samples).

FIG. 8 is an SEM image of a cross section of an experimental CBRAM stack20 according to an embodiment of the present disclosure. The CBRAM stack20 included a bottom electrode 22 of tungsten, a dielectric material 23of silicon nitride, an active material 26 of zirconium oxide, an ionsource material 27 including copper and tellurium, and a top electrode29 of silicon-rich tungsten silicide. The silicon-rich tungsten silicideincluded a Si:W ratio of between about 2.4:1 and about 2.6:1. Eachmaterial was formed at a thickness of between about 200 Å and about 300Å, except for the active material 26, which was formed to a thickness ofabout 20 Å. The CBRAM stack 20 was heated to a temperature of about 270°C. to simulate subsequent processing conditions. The substitution ofsilicon-rich tungsten silicide in the top electrode 29 in place of thetungsten of the top electrode material 19 (FIG. 7) enabled the CBRAMstack 20 to maintain its substantially planar shape, as can be seen inFIG. 8. Furthermore, the thickness of the ion source material 27 issubstantially uniform. Due to the planarity of the top electrode 29 andthe uniformity of the ion source material 27, the CBRAM stack 20 may bereadily etched, and devices (e.g., CBRAM cells) formed from the CBRAMstack 20 may be operable.

Without being bound to a particular theory, it is believed that thesilicon atoms of the silicon-rich tungsten silicide of the top electrode29 may be available for reacting with at least one element of the ionsource material 27 to provide improved intermixing of materials acrossan interface between the top electrode 29 and the ion source material27. The materials at the interface may be chemisorbed rather thanphysisorbed. In addition, the tungsten silicide of the top electrode 29may exhibit lower internal stress compared to a top electrode formed oftungsten.

FIGS. 9 and 10 are graphs showing elemental concentrations inexperimental CBRAM stacks, such as those shown in FIGS. 7 and 8,respectively, as a function of location in the CBRAM stacks. The graphof FIG. 9 was generated by measuring the concentration of the variouselements in the materials of a CBRAM stack having a tungsten topelectrode, similar to the CBRAM stack 10 shown in FIG. 7. The graphshows the concentration of the various elements in the materials in theCBRAM stack including a silicon nitride dielectric material (shown bythe relatively high concentration of Si/W and N from about 10 nm toabout 15 nm), a zirconium oxide active material (shown by the spike inZr at about 21 nm), a copper-tellurium-germanium ion source material(shown by the relatively high concentration of Cu, Te, and Ge betweenabout 22 nm and about 50 nm), and a tungsten top electrode (shown by therelatively high concentration of Si/W between about 50 nm and about 70nm). As can be seen in the graph at about 50 nm, the tungsten of the topelectrode and the copper of the ion source material overlap over a rangeof only about 2 nm to about 4 nm. The slope of the Si/W line betweenabout 50 nm and about 58 nm is steep, indicating little intermixing ofthe copper and tungsten across the interface between the ion sourcematerial and the top electrode. The materials at the interface may bephysisorbed.

The graph of FIG. 10 was generated by measuring the concentration of theelements in the various materials of a CBRAM stack having a tungstensilicide top electrode, similar to the CBRAM stack 20 shown in FIG. 8.The graph shows the concentration of the elements of the variousmaterials in the CBRAM stack including a silicon nitride dielectricmaterial (shown by the spike of Si/W and N from about 10 nm to about 15nm), a zirconium oxide active material (shown by the spike in Zr atabout 20 nm), a copper-tellurium-germanium ion source material (shown bythe relatively high concentration of Cu, Te, and Ge between about 22 nmand about 48 nm), and a tungsten silicide top electrode (shown by therelatively high concentration of Si/W between about 42 nm and about 70nm). As can be seen in the graph at about 47 nm, the tungsten silicideof the top electrode and the copper of the ion source material overlapover a range of about 8 nm to about 10 nm. Comparing the region ofoverlap of the graph in FIG. 10 with the region of overlap of the graphin FIG. 9, it can be seen that the materials of the top electrode and ofthe ion source material of the graph in FIG. 10 intermix more readilyacross the interface between the top electrode and the ion sourcematerial than in the graph in FIG. 9. In addition, the slope of the Si/Wline between about 47 nm and about 51 nm of FIG. 10 is less steep thanthe slope of the corresponding portion of the Si/W line in FIG. 9,indicating intermixing of the materials of the top electrode and of theion source material. Accordingly, without being bound to a particulartheory, it is believed that the use of the metal silicide in the topelectrode enables greater intermixing of the materials of the topelectrode and of the ion source material across the interface betweenthe materials and, accordingly, improves adhesion between these twomaterials. The materials at the interface may be chemisorbed. Inaddition, the top electrode of metal silicide may have a reducedinternal stress compared to a top electrode formed of a pure metal(e.g., tungsten). By way of example and not limitation, a tungstensilicide material may have an internal stress that is about one thirdthe internal stress of a tungsten material.

With reference to FIG. 11, illustrated is a simplified block diagram ofa memory device 500 implemented according to one or more embodimentsdescribed herein. The memory device 500 includes a memory array 502 anda control logic component 504. The memory array 502 may include aplurality of CBRAM cells 100, as described above. The control logiccomponent 504 may be configured to operatively interact with the memoryarray 502 so as to read, write, or refresh any or all CBRAM cells 100within the memory array 502.

Accordingly, a memory device comprising a memory array is disclosed. Thememory array comprises a plurality of memory cells (e.g., CBRAM cells100). Each memory cell of the plurality comprises a top electrode thatincludes a metal silicide.

With reference to FIG. 12, illustrated is a simplified block diagram ofa system 600 implemented according to one or more embodiments describedherein. The system 600 includes at least one input device 602. The inputdevice 602 may be a keyboard, a mouse, or a touch screen. The system 600further includes at least one output device 604. The output device 604may be a monitor, touch screen, or speaker, for example. The inputdevice 602 and the output device 604 are not necessarily separable fromone another. The system 600 further includes a storage device 606. Theinput device 602, output device 604, and storage device 606 are coupledto a conventional processor 608. The system 600 further includes amemory device 610 coupled to the processor 608. The memory device 610includes at least one CBRAM cell, such as the CBRAM cell 100, accordingto one or more embodiments described herein. The memory device 610 mayinclude an array of CBRAM cells. The system 600 may be incorporatedwithin a computing, processing, industrial, or consumer product. Forexample, without limitation, the system 600 may be included within apersonal computer, a handheld device, a camera, a phone, a wirelessdevice, a display, a chip set, a game, a vehicle, or other knownsystems.

Accordingly, a system is disclosed comprising a memory array comprisinga plurality of memory cells (e.g., CBRAM cells). Each memory cell of theplurality comprises a top electrode including a metal silicide.

An apparatus (e.g., a memory device 500, a system 600 including a memorydevice 610) is also disclosed including a plurality of memory (e.g.,CBRAM) cells. Each memory cell of the plurality of memory cells of theapparatus includes a first electrode, an active material over the firstelectrode, an ion source material over the active material, and a secondelectrode including metal silicide over the ion source material. Themetal silicide of the second electrode of each memory cell may be asilicon-rich metal silicide. Each memory cell of the apparatus may alsoinclude an adhesion material at an interface between the ion sourcematerial and the second electrode.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, the disclosure is not intended to be limited to the particularforms disclosed. Rather, the disclosure is to cover all modifications,combinations, equivalents, and alternatives falling within the scope ofthe disclosure as defined by the following appended claims and theirlegal equivalents.

What is claimed is:
 1. A memory cell comprising: a first electrode; anactive material in electrical contact with the first electrode; an ionsource material over the active material; and a second electrodecomprising a metal silicide over the ion source material.
 2. The memorycell of claim 1, wherein: the metal silicide of the second electrode issilicon-rich and comprises at least one of tungsten silicide, titaniumsilicide, cobalt silicide, tantalum silicide, manganese silicide,ruthenium silicide, and nickel silicide; and the ion source materialcomprises a chalcogenide material and copper.
 3. The memory cell ofclaim 1, further comprising an adhesion material comprising at least oneof silicon and a metal silicide disposed between the ion source materialand the second electrode.
 4. The memory cell of claim 3, wherein thesecond electrode comprises tungsten silicide and the adhesion materialcomprises silicon.
 5. The memory cell of claim 1, wherein the metalsilicide of the second electrode comprises a homogeneous silicon-richmetal silicide.
 6. The memory cell of claim 1, wherein the metalsilicide of the second electrode comprises a silicon-rich metal silicidehaving a variable concentration of silicon across a thickness of thesecond electrode.
 7. The memory cell of claim 1, wherein the activematerial comprises at least one of a transition metal oxide, an aluminumoxide, a silicon oxide, and a chalcogenide material.
 8. The memory cellof claim 1, wherein the ion source material comprises copper and atleast one of tellurium and germanium.
 9. The memory cell of claim 1,further comprising a dielectric material between the first electrode andthe active material, the dielectric material having an openingtherethrough filled at least partially with a conductive materialproviding electrical contact between the first electrode and the activematerial.
 10. A memory cell, comprising: a first electrode; an activematerial in electrical contact with the first electrode; an ion sourcematerial on a side of the active material opposite the first electrode;a second electrode formed of an elemental metal on a side of the ionsource material opposite the active material; and an adhesion materialincluding a metal silicide positioned between the ion source materialand the second electrode, the metal of the metal silicide and theelemental metal of the second electrode being the same element.
 11. Thememory cell of claim 10, wherein: the second electrode comprisestungsten; and the adhesion material comprises a silicon-rich tungstensilicide.
 12. An apparatus comprising: a plurality of memory cells, eachmemory cell of the plurality of memory cells comprising: a firstelectrode; an active material over the first electrode; an ion sourcematerial comprising a metal over the active material; and a secondelectrode comprising a metal silicide over the ion source material. 13.The apparatus of claim 12, wherein the metal silicide of the secondelectrode comprises a silicon-rich metal silicide having a higherconcentration of silicon in a region of the metal silicide proximal tothe ion source material.
 14. The apparatus of claim 12, wherein eachmemory cell of the plurality of memory cells further comprises anadhesion material at an interface between the second electrode and theion source material.
 15. The apparatus of claim 14, wherein the adhesionmaterial comprises one of the metal silicide and silicon.
 16. A methodof forming a memory cell, comprising: forming a first electrodecomprising a conductive material; forming an active material over and inelectrical contact with the first electrode; forming an ion sourcematerial over the active material, the ion source material comprising achalcogenide material and a metal; and forming a second electrodecomprising a metal silicide over the ion source material.
 17. The methodof claim 16, wherein: forming an ion source material comprises forming acopper-tellurium material, a copper-tellurium-germanium material, or acopper-tellurium-silicon material; and forming a second electrodecomprising a metal silicide comprises forming a second electrodecomprising tungsten silicide.
 18. The method of claim 17, whereinforming a second electrode comprising tungsten silicide comprisesforming a homogeneous, silicon-rich tungsten silicide material.
 19. Themethod of claim 18, wherein forming a homogeneous, silicon-rich tungstensilicide material comprises forming a tungsten silicide material havingbetween about 2.1 silicon atoms per tungsten atom and about 3.5 siliconatoms per tungsten atom.
 20. The method of claim 17, wherein forming asecond electrode comprising tungsten silicide comprises forming aheterogeneous tungsten silicide material having a higher concentrationof silicon in a portion of the second electrode proximal to the ionsource material.
 21. The method of claim 16, further comprising formingan adhesion material comprising at least one of silicon and a metalsilicide at an interface between the second electrode and the ion sourcematerial.
 22. A method of adhering a material including copper and amaterial including tungsten, the method comprising: forming a firstelectrode on a substrate; forming an active material in electricalcontact with the first electrode; forming a material including copperover the active material; forming a tungsten silicide material over thematerial including copper; and treating the material including copperand the tungsten silicide material to intermix at least one of copperfrom the material including copper, tungsten from the tungsten silicidematerial, and silicon from the tungsten silicide material across aninterface between the material including copper and the tungstensilicide material.
 23. The method of claim 22, wherein forming thematerial including copper comprises forming a chalcogenide materialincluding copper.
 24. The method of claim 22, wherein forming a tungstensilicide material comprises forming a substantially homogeneoussilicon-rich tungsten silicide material.
 25. The method of claim 22,wherein forming a tungsten silicide material comprises forming asilicon-rich tungsten silicide material with a higher concentration ofsilicon in a region of the tungsten silicide material proximal to thematerial including copper.
 26. The method of claim 22, furthercomprising forming an adhesion material comprising one of silicon andtungsten silicide over and in contact with the material including copperand wherein forming a tungsten silicide material comprises formingtungsten silicide over and in contact with the adhesion material.